Semi-analytical calculations of the neutron noise in 2-group theory for 1-D homogeneous systems

In this paper, 2-group diffusion and P1 theories are compared via semi-analytical calculations of the neutron noise in a 1-D 2-region slab reactor using the Green's function technique. The neutron noise, i.e. the time variations of the neutron flux around its mean value, is useful for core diagnostics and monitoring of a reactor. For a 2-region system, the Green's function can be calculated in a semi-analytical manner as a function of frequency and space, for various positions of the perturbation. This work demonstrates that for practical situations in a Light Water Reactor, there is no significant advantage to use P1 theory since diffusion theory gives acceptable results. The largest deviations between the two formalisms are observed in the reflector region. This study also shows that neglecting the effect of cross-section perturbations on the diffusion coefficient has a rather strong impact on the solution in the reflector. (authors)